A British soldier was killed on foot patrol in Afghanistan today, the Ministry of Defence said.

His death takes the number of British service personnel killed in Afghanistan since operations began in 2001 to 150.

The soldier, from the 2nd Battalion, Royal Welsh Regiment, was injured in an explosion in Musa Qala district centre, in northern Helmand province. Medics worked to save him but he died at the scene.

The spokeswoman for British troops in Afghanistan, Commander Paula Rowe, said: "Task Force Helmand feels the loss of every serviceman and we mourn the death of this brave soldier. We send our thoughts and prayers to his family and friends at home and all those who served alongside him at this desperately sad time."

The soldier's next of kin had been informed but a 24-hour grace period was in place before he would be officially identified, the MoD said.

Brigadier-General Richard Blanchette, the spokesman for the International Security Assistance Force (Isaf), said: "We are saddened by this brave soldier's death, and offer our heartfelt condolences to the soldier's family and friends. Through our grief, we are strengthened in our resolve to help bring security and stability to Afghanistan."

The news of the death came as the MoD described how a Royal Marine had foiled a roadside bomb plot.

While on guard duty he spotted three men digging on a track near a British army base in Sangin, northern Helmand. The commando, from 45 Commando Group, became suspicious when he noticed local people avoiding the area.

Thinking they were hidden from sight, the three men were preparing a hole to plant a roadside bomb. One of them had an explosive device attached to a pressure plate trigger, similar to several bombs used by Taliban fighters which have killed soldiers as well as civilians.

After ensuring no one was nearby, the marine used a shoulder-launched missile to kill the three men and destroy the device.

Commander Rowe said the men were planting the bomb on a route used by ISAF, the Afghan national security forces and civilians.

"These devices are totally indiscriminate and it is highly likely that if it had detonated, it would have been innocent people from Sangin who would have been killed or injured.

"The Taliban have been forced to use these cowardly devices, showing no regard for life. An accurate strike by Isaf forces prevented this device being laid and protected the local population, causing no damage or injuries to anyone other than those enemies of Afghanistan who were attempting to lay it."